Were the Boeing 787 Batteries Cooled Properly?

Whether or not the battery exceeded its design voltage, however, experts believe a cooling system was critical. Lithium-ion battery chemistries in general are "energetic," they said, and the cobalt oxide varieties of lithium-ion are particularly so.

"Not all lithium-ion batteries are created equal," Cosmin Laslau, a research analyst for Lux Research, told us. "None of them should fail. They are all essentially safe. But in the event of a failure, lithium cobalt oxide would fail earlier than the other types. Chemical bonds in lithium cobalt oxide will release oxygen earlier." Experts say the release of that oxygen can, in rare cases, lead to fire.

Many engineering teams around the world choose cobalt oxide chemistries, however, because it offers energy densities that can be up to 25 percent higher than other types of lithium-ion, such as manganese spinel (used in the Chevy Volt) and phosphate-based systems.

To counteract the higher energies, big, lithium-ion batteries in general are often used in conjunction with cooling systems, no matter whether they are cobalt-, manganese-, or phosphate-based. The Chevy Volt, for example, employs liquid coolant that circulates through 1-mm thick channels machined into 144 metal plates sitting between its lithium-ion manganese spinel cells. Similarly, the Prius PHV plug-in hybrid uses specialized fans, intake ducts, and 42 temperature sensors to actively monitor and cool its lithium-ion battery.

To be sure, the 787's 63-lb battery pack is smaller than those of today's typical electric cars, which can often exceed 400 lb. But experts said that lithium-ion batteries of all types need ways for heat to get out. "Size does make a difference," Cairns told us. "But the size of that (Boeing) battery is still substantial. If the cell casings are touching one another or have inadequate space to allow for natural convection cooling by air, then you're in for trouble."

Cairns said that he hadnít personally seen the Boeing battery pack, however, and didn't know if Boeing engineers had provided any means for the heat to escape.

Battery experts who spoke to Design News repeatedly stressed the fact that all types of lithium-ion batteries can be safe and successful, if engineered properly. The question still being answered is whether Boeing engineers did that. ďThey should have stress-tested the battery with charging system as it it is installed in the 787,Ē Sadoway said. ďI myself wouldn't fly in a 787 at this point."

The lack of a cooling system would be very puzzling. According to a friend of mine who is a battery guy, lithium ion batteries are the highest energy density and are one of the most volatile chemistries, so correct charging and cooling are of paramount importance.

Not so puzzling. Before you design in a cooling system, you ask how high can you go without it. For example, if a transistor is rated with a junction temperature of 150 degrees, I would let it heat up to 100 degrees before I put a fan in. Thats a 33% margin. Cooling at sea-level is not the same as cooling at 8000ft equivalent alitude in a pressuized airliner, though.

Battar, your principle is sound but the article suggests that the cooling system may have been inadequate. Seems to me they might not have asked the question properly...and in a critical application safety margins for proper operation would be pretty important.

Many Lithium ion batteries are not actively cooled but do manage not to burst into flames. Most laptop batteries, camcorder batteries, etc., manage to function without active cooling.

Looking at the photos of the Boeing 787 battery pack I can only make out a single pair of high current output pins that ties the battery to the aircraft's power bus. If so, then all charging and discharging is going through that single pair of contacts, which means the cell monitoring and charging circuitry must live inside the battery. So, if the battery got too hot, possible runaway condition, it could have fried the controller thus disabling any chance of shut down or external alarm.

It would be foolish to not have additional wiring to enable external monitoring and control of the pack. Virtually every Lithium ion camcorder battery communicates with its host as do many other consumer and professional battery packs.

Not having active cooling and external monitoring of system temperature for an aircraft battery system would seem foolhardy.

It looks like control electronics reside inside the battery pack, so yes they would be subject to rising temperatures AND if electrolyte sprays on the control board all bets are off. This does not appear to be an intrinsically safe design.

Chuck, do you get a sense that perhaps Boeing moved to the cobalt oxide cathode lithium-ion batteries to shed weight and then made a decision to not include a cooling system that would have added net weight? It is feasible that this type of failure is only found after the 787 is used in process and not in testing and that Boeing can find a safe fix. Gosh, I sure hope that it does not turn out to be known, debated cost-saving management decision that turns political...

Good point William. I wonder if the energy density of the lithium-ion battery system with an additional cooling system would now be less-favorable than the energy density of the traditional/proven battery technology (without the additonal cooling system).

It's possible the cooling was 'built-in', i.e. the design current draw and subsiquent heat load was lower than the thermal capacity of the unit as installed. That's how zillions of the small and ubiquitous lithium batteries consumers use every day work. It'll be interesting to see how this story plays out. Certainly some mistake was made somewhere, but we seem to be jumping to conclusions

The division I worked for several years ago had a similar Lithium-ion battery 'thermal event' on a much smaller scale in a consumer market portable radio... We did not experience any fire, but there certainly was sufficient energy released to create a lot of smoke and reduce the radio to a bubbling mass of melted plastic. The cause seemed to be a short resulting from insulating materials being capable of sliding with vibration... The entire experience was perplexing...the experts were telling us it couldn't happen, yet it was!

The weight savings was a big temptation so they calculated the risks and made a decision to go with this battery.

The surprise came in real life when the battery ended up working much harder than anticipated. Accessories?, add-ons?, custom build? (Sales says yes, yes, yes, and the original engineer isn't even in the picture.)

I was a Boeing Engineer for a while and I worked on the 767 and 777 projects. I know something about Boeing. Yes, weight savings is very important. BUT SAFETY is the highest priority. So high, in fact that no technology is used that has not been thoroughly tested and confirmed to be safe. I really don't understand why this is happening, (and I will not guess, as I am an ME) we will find out eventually. Oh and yes, "The original Engineer isn't even in the picture" is somewhat true. Once an engineering design is completed by "The original Engineer" The design is circulated through all the engineering departments for their blessing, and modification (if any) before it is allowed to be installed in an airplane. The design may or may not look like the original after everyone has gotten their hands on it.

Boeing will suffer politically, regardless of the decisions they make now. Their best option is to have a replacement strategy defined and a timeline for implementation & FAA approval before the end of this week. Any more delay will cripple their Dreamliner, giving the A380 a huge advantage.

This was a massive integration effort with literally thousands of verification tests. Notwithstanding it's relative criticality, if this is the biggest issue Boeing can pat themselves on the back, but (as previously mentioned) they must move expeditiously to arrest the problem, accept full culpability, and implement a lasting fix before their market share begins to suffer. The Defense industry has thought me that these post-production woes are intrinsic in a project of this magnitude; thank God the problem was discovered without catastrophic consequences.

nelso7926, I agree completely. No injuries and certainly no fatalities. I'm sure Boeing has tested and retested this system so I would certainly hope the issue is inadequate cooling and not the lack of cooling. With that being the case, are all of the failures on the ground? Are any experienced in flight? Also, can anyone tell me if there are redundant systems for this device? I don't think so but do not know.

Virtually everyone agrees with you at this point, Jenn -- NTSB, most newspapers and experts. Even USA Today even did an editorial calling for the 787 to be grounded until the problems are fully understood.

We're working at the grass roots level with lithium systems in E-Scooters and we're having our problems although not quite as dramatic as Boeings. The battery management system does what it's supposed to do where temperature increases beyond a certain level opens the circuits...somewhat inconveniently after about 3 blocks of hard acceleration. Troubleshooting indicates that by disconnecting the battery, pausing, then reconnecting resets the system, and as long as a reasonable acceleration is the input the system works continuously. As soon as a higher torque (hence amperage increase) is applied to the drive system over a certain length of time the system cuts out. Our solution to this irritation is in work consisting of a hybrid battery system using lead acid for acceleration and lithium for cruise, the controller being rigged to accomodate the changes. Boeing's solution may be the same in the long run...cooling systems are just another aggravation, but hybrid battery systems rigged through a reliable controller may be slightly heavier but likely not as heavy as a cooling system and have the advantage of no dead weight (all batteries being functional)

There is someting fishy,for decades I have used embedded temperature sensors in all batteries, it is a part of my designed cell balancing and battery management systems, surely sudden temperature surges would be recorded -of course it will not prevent explosion due to O2 accumulation. I have seen cost saving measures causing accidents -but in aerospace!!

That's a scary thought, Bill. It's not hard to imagine Boeing deliberately choosing cobalt oxide for the higher energy density. That's its chief advantage over other lithium-ion chemistries and it's the reason many engineers choose that chemistry. But as for their alleged lack of a cooling system: It's anybody's guess. I think a lot of engineers are still climbing the learning curve when it comes to all the lithium-ion chemistries.

I share your scary thought, Chuck. I will always give Scientists and Engineers the benefit of the doubt, but as we are remembering the 27th anniversary of the loss of the Challenger's Crew today, sometimes margins of risk get bundled together into an "acceptable flight risk". Not suspecting anything nefarious, but with such a complex system, sometimes it is only possible to rank relative risk in hindsight.

It would seem that not enough is known about the characteristics of this chemistry when used in aircraft systems where high altitudes are encountered. If a cooling system is deemed necessary, it will require redundancy for safety purposes. This of course will require futher testing and approval by the FAA for airworthyness. Perhaps a step back to a known and proven battery technology could be used temporarily at the cost of reduced capacity, but at least it will get the aircraft flying once again until a new, improved battery design can be readied.

The litium battery must be observed in its used enviroment. We are talking low atmospheric pressure and the batteries could be outgassing causing a rupture between layers. Include with that plane vibration from jet engines could play in deterioating loose layers within the battery. The colder temperature at that altitude could have cause contractions the batteries should not have seen. As I remember the batteries should have thermal monitoring device and balance circuits to prevent heavy discharge and charge. So Rapid short within the batteries due to enviromental such as atmospheric condition not designed into the battery compartment would give a clue why the thermal sensing did not have time to respond and shut down.

You cannot analyze this by the damaged batteries alone. And new set for enviromental testing needs to be done to characterize the destruction.

Very good point, Paul. Elton Cairns of the University of California agrees with you. He told us that the higher, colder altitudes were a detriment, not an advantage in this situation. Cairns, by the way, should know: He designed the PEM fuel cells for the Gemini spaceflights in the 1960s.

Ougassing should have been observed during tests. True, low atmospheric pressure might accelerate outgassing but the atmospheric pressure inside a (pressurized) commercial aircraft cabin is generally in the range of normal.

I've always assumed that large commercial aircraft capable of cruising at high altitudes had some way of boosting cabin pressure, and if so why not go to full atmospheric? But in my experience, pressure does noticeably increase during a descent (ear problems), so you may be right, it's allowed to drop well below atmospheric. Even so, vibration is still the logical culprit.

Cabin altitude (internal cabin pressure at altitude) for the 787 is 6,000 feet maximum. Plane cabins are not usually pressurized to sea level at altitude because of the stress on the airframe, although there is a trend to increase cabin pressures. 8,000 feet cabin altitude is generally the minimum pressure.

Yes, the analysis needs to examine undamaged batteries from the same manufacturer and date code. Preferably samples that have already seen some use. In my own experience with medical devices - yes they need to be highly reliable as well - battery manufacturers want to offer their standard processes even for custom batteries. The problem here is that they want you to take RoHS compliance and No-Clean solder systems. This leads to unreliable circuitry when exposed only to thermal and humidity cycling. Add stress associated with a high vibrational environment and the reliability slips even lower.
I'm certain that Boeing did a lot of testing and much of it done in parallel in an attempt to minimize schedule slip. Unfortunately, some problems only reveal themselves when certain of the stressors are tested in series - just as they are experienced in the real world and under electrical load.
The other aspect of testing that is critical here is the pass-fail criteria. Simply meeting operating specs isn't good enough at this point. The investigators need to gently disassemble the units and along with everything else examine the circuitry under 20x to 40X magnification looking for the beginnings of electrochemical issues such as surface salts, dendrites and the more difficult to detect, tin whiskers. You will be hard pressed to find a component these days that doesn't have pure tin on the leads.
A problem like this rarely has a single cause. To or more corner case conditions must come together in just the right way. This is why serial testing of multiple assemblies under operational load is necessary.

If this is true, then it's a bit scary to think this could happen again. Let's hope engineers get the battery chemistry right next time so something like this doesn't happen again and cause an even more dangerous situation.

They will get it right eventually, Liz. But it could take a while. Over the weekend, CNET published a story in which they, too, interviewed Donald Sadoway of MIT. Sadoway told them that the problems could keep the 787 fleet grounded until 2014.

FYI, Elizabeth, in case you missed it, there was a lot of criticism of composites in aircraft early in the game last year due to some minor problems with the 787's composites, as well as composite issues with some Airbus planes.

The answer's complex. Boeing wasn't exactly forthcoming about details and there were many, many news items, much of it speculation. This article, and its comments board, might give you some idea. http://www.designnews.com/author.asp?section_id=1392&doc_id=238056

@Ann: On the other hand, a pessimist would say that the battery problems are just keeping the planes from accumulating enough flight time for the problems with the structural composites to become apparent yet. Fix the battery problems and get the planes flying again -- for long enough to get some fatigue cracks going -- and pretty soon you'll have structural components failing.

I'm not saying that I necessarily endorse that view, but that's the way you need to think if you want your designs to work.

You hit on the long term problem. The composites have not had enough in-use time to verify long term durability. Accelerated testing, which has been done on the types of composites used in aircraft, is useful, but not definitive. The best accelerated testing is achieved when the results can be checked against a known record accumulated in the actual operating enviroment. That has not yet been possible at the depth and scale of the current expansion of composites usage.

Given the importance of this issue to Boeing, I would be shocked if it kept the 787 down until 2014. That would be a major setback to a very high profile program. But I also think their engineers will also be very careful in avoiding missteps in implementing a solution to this problem. Not an easy thing to have the world watching while you solve a complex technical issue.

I can't believe Boeing would use a battery design that was not so carefully bench tested that there was absolutely no way it could overheat no matter what happened to the charging circuit and no matter how little cooling was available.

On the other hand it is quite possible that due to vibration in the aircraft, the electrodes might go into a vibrational resonance allowing a couple to touch each other and cause an internal short. This could be difficult - but not impossible - to simulate on the bench.

I am with you on this, but obviously something went wrong. Even in the most careful design, sometimes there are unforseen problems. Then again, it's pretty well known that lithium ion batteries can overheat and possibly explode...so I guess it will take awhile before we know the real story.

From My earlier comment on these Lithium batteries, I want to hear from Boeing that these batteries are not COTS purchased batteries from the CLINTON era for purchase COTS to save money... Off the shelf devices DO NOT WORK ANYWHERE except on earth in a typical building. Now I want to see evidence that these batteries went through some BOEING testing and was accepted as properly built components worth of aircraft flight for 20 years in service. I bet they dont have that information available and this gets settled out of court with Uncle Sam!!

Paul I am far more optimistic on this one! I simply cannot believe that Boeing who has lived by the DO 254 credo for the better part of its existence could ever opt for standard COTS without rigourous climatic testing to verify the specs were met or exceeded. This would constitute a watershed in unacceptably poor risk management and I am not prepared to take away the benefit of the doubt, at least not just yet. If you are correct then we can both share the same kleenex in a corner, but I simply cannot believe that scenario.

I like how everyone is assuming that active cooling is needed (and they seem confident about this.) However nowhere in the article is there a statement of current input or current output. We do not know the amount of power going in or out and cannot make an educated guess if active cooling is needed. I am sure if they were drawing a few W's an hour out of that battery the sheer size alone will handle cooling. There is a sentence that states that current input and output is controlled which leads me to believe that the battery had sufficient cooling.

Any equipment that goes into a plane is tested for thermal cycles. Not saying this one was only reviews of the reports can prove that. But I will be surprised if it was an engineering flaw and it had anything to do with cooling. If I took a guess it would have to be the rest of the electrical system has a fault. it could be one item or multiple items.

However on a project of this scale and expense and complexity it would be wise to not guess and wait for the investigators to do their job and inform the rest of the world what the problem is.

Ervin is quite right! Besides that, any design that required active cooling for reliable operation would be a very poor choice in a situation where reliability and safety are top priority. Just look at the Japanese nuclear plant failure as a verification of that concept!

In addition it is certain that the folks at Boeing had verified that the design had an adequate margin of safety. So that would put the cause of failure in the supplier quality area, which, as has been reported quite a few times in Design News over the years, has been one of the ongoing problems with the project. Unfortunately, just because we have provided detailed and adequate specifications for items to be provided by suppliers does not assure that those specifications will always be met.

William K, you bring up a good point about specs and suppliers. Unless you do a lot of quality control on those suppliers, you open yourself up to potential problems.

Years ago I was at a spacecraft manufacturer. We had a ball bearing lab. Yes, ball bearings. These are used in gyroscopes, reaction wheels and other mechanisms. We did start to contract that out, but the quality was so bad that we brought it back in house. It was that important. Not long ago I talked to a local manufacturer of components for industrial machinery. His supplier convinced him to take some foreign made ball bearings. Well, they failed in customer installed equipment in a matter of months. He could test for most things, but did not have the facility to test for hardness. Guess what the problem was?

I could go on and on about companies that I have consulted with that contracted out manufacturing and were burned by it. Generally the smaller companies go out of business. Boeing's experience with the 787 is a cautionary tale. An aircraft manufacturer is not just a brand and design house. Some of the people posting here have said they would not fly in a 787. These are informed people. Boeing has some work to do.

It's true that we don't know yet what current or voltage was going in or out of the battery. But electronic battery management -- i.e., protection against overvoltage and overcurrent -- by itself is not considered sufficient for cooling of a big lithium-ion battery, the experts told us. "Just having protective circuits is fine, but it's absolutely insufficient," Elton Cairns of the University of California said when we asked him. "There's no avoiding the generation of a certain amount of heat. Ant time you operate a battery, heat is generated." It's worth noting that all automakers who use lithium-ion batteries also also use battery management ICs to monitor voltage, current and charging rate. But even while they use battery management ICs, they also all use cooling systems -- either liquid-based or air-based.

I checked the CT scans made by NTSB and I'm surprized to see the deformation of the individual cells. The protective cell case looks weakly designed when the requirments for aeronautical applications include strong external pressure variations. I would say also that the large terminals could initiate case cracks during battery assemby or life time.

I would not tip on battery manufacturing process issues much more on battery cell integration solutions. It looks like a poor engineering solution.

I guarantee you that was not expert advice. Protection circuits are placed to insure that the amount of power drawn from a battery allows for safe operation. True we would like to have active cooling but:

Can any one guess the cost of heat sinks?

The added weight because of the heat transfer unit?

The cost of the delivery of Air, water, or fluid flow through the device (added weight as well)?

The cost of developing and testing the equipment so that it will not impact safety of the system during operation in the event of a failure?

The cost of maintaining the equipment?

No I don't think there is any logic in the claim that active cooling is required simply because other systems tend to use it. Best and cheapest way is to hire an engineer specializing in thermal characteristics of that device and insure that heat rise of the internal components does not pose a threat to the system and limit power draw that way. You supply more deep cycle power for less weight (weight is a major factor in aviation and duration of emergency operation) and insure that your device has passive cooling. This is a guess and it seems that the end design goal to this battery was this. I have dealt with devices that require active cooling in the airframe (I specialize in the hottest part of the airplane the engine). Testing components that require active cooling is a long stretched process. The analysis of the heat transfer unit alone could easily become a 1000 page report. Not to mention the cost added to the unit.

I agree, don't jump to conclusions. It would be difficult to find a generic design flaw that was so carefully balanced that only two batteries have destructed out of the one hundred batteries in the fifty delivered airplanes. I would expect dozens of battery fires if the heat dissipation was ignored as in "you have to use active cooling". To me it seems that the apparent rarity of problems seems to fit some less obvious design flaw or a quality assurance problem.

Just a word about the composite construction. Take a look at the carbon composite B-2, in service since 1997. I don't think carbon composites are a new thing to Boeing.

It seems to me that the battery problem on the 787 is the result of engineering being pushed too far too fast. Now that the problem is out in the open many "experts" are saying it's the cooling system. It sounds like this common knowledge about the characteristics of the 787 batteries. If so, why did the engineers go ahead and not put a cooling system in? No time? There was a schedule to meet? It's a monir problem? Good engineers solve these problems,given enough time.

Technology has become too complex and there are a lot of pitfalls in almost everything but especially so when new technology is introduced. Analysis and deliberation takes so much time that management becomes impatient. Most companies have replaced team managers with semi-technical or pseudo technical schedule pushers with the philosophy that ignorance is bliss when schedules have to be met. After all the world is very competetive and risk taking has become the name of the game. But not having a back up plan such as an alternative battery pack design which may be more reliable though somewhat less efficient is a serious incompetency issue. Boeing would be lucky if the cause can be determined with certainty and even if it is determined, the increased scrutinity will not allow immediate release of the fix. The finacial damage cused by the delay is far out of proportion to the benefit of the new battery.

It seems to me that the battery problem on the 787 is the result of engineering being pushed too far too fast. Now that the problem is out in the open many "experts" are saying it's the cooling system. It sounds like this common knowledge about the characteristics of the 787 batteries. If so, why did the engineers go ahead and not put a cooling system in? No time? There was a schedule to meet? It's a monir problem? Good engineers solve these problems,given enough time.

I think you're right on the money when you say that good engineers solve these problems, given enough time, Gorksi PE. Occasionally, there are mistakes, but engineers know how to handle high-energy situations. Gasoline holds far more energy than lithium-ion batteries, and it seems like engineers have mastered the safety of the internal combustion engine.

Has anyone considered the lack of adequate convective cooling at cruising altitude? I used to work at Los Alamos in the 80s and several devices designed at sea level would fail due to overheating at the 7700 feet altitude arising from the lower air density, especially CRT computer terminals.

I don't know if there was any official mention of it, lcs1956. However, in one of our subsequent articles, Elton Cairns of Lawrence-Berkeley labs said this: "When the plane is at altitude, the air is less dense," he told us. "So even if it's cooler, the less dense air may not have adequate heating capacity to provide enough cooling for the battery. If they don't have active cooling, then I question the adequacy of the cooling arrangement."

A few weeks ago, Ford Motor Co. quietly announced that it was rolling out a new wrinkle to the powerful safety feature called stability control, adding even more lifesaving potential to a technology that has already been very successful.

It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.

People who want to take advantage of solar energy in their homes no longer need to install a bolt-on solar-panel system atop their houses -- they can integrate solar-energy-harvesting shingles directing into an existing or new roof instead.

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